VCV Rack directly conforms to the visual patterns and usage patterns of Eurorack hardware, so I'd guess that is the main reason that it's so popular relative to those other options. PD is also a bit harder to get going with out of the box, even with packages like Automatonism, impressive though they are.

Reaktor 6 had a similar thing happen, lots of people who hadn't used it before were brought into that ecosystem by their "blocks", which also kinda emulate Eurorack.

The Fundamental modules included with Rack and all other VCV-branded modules are designed by Grayscale, also responsible for the panel design of a dozen Eurorack manufactures on the market. http://grayscale.info/design-services/